Pipe having external threaded ends are manufactured in a wide variety of lengths, diameters, wall thicknesses, thread dimensions, and materials. The maximum length of individual sections of large diameter pipe for industrial use is generally about thirty to forty feet because of constraints in transporting the pipe from the point of manufacture to the point of use. When a very long pipe is needed, it is generally constructed by connecting multiple sections of pipe with short sleeves having internal threads known as couplings. It is common for pipe manufacturers to ship sections of pipe with a coupling already connected to one end (referred to herein as a pipe section—coupling assembly). FIG. 1 shows a section of pipe 1 and a coupling 2 before connection. FIG. 2 shows the section of pipe and coupling connected together for shipment.
Pipes having lengths of thousands of feet are commonly constructed in this way for use as drill pipe, tubing, conductor pipes, and casing in the oil drilling industry. The pipe sections and couplings are sometimes referred to as oil field tubular goods (OFTG) or oil country tubular goods (OCTG). The pipe sections and couplings have diameters of about two inches to three feet. Diameters of about 6 inch are the most common. The American Petroleum Institute (API) and other organizations have established standards for such products.
The external (male) threads of the pipe and the internal (female) threads of the coupling of a pipe section-coupling assembly can be damaged by impact during shipment and by corrosion if exposed to the elements for a long period of time. If the threads are damaged, the affected pipe or coupling may be difficult or impossible to connect. To prevent damage, pipe manufacturers commonly install cap-like protectors on the free ends of the pipes (commonly known in the oil industry as the pin end) and plug-like protectors into the open ends of the couplings (commonly known in the oil industry as the box end). The terms “pin end thread protector” and “box end thread protector” are used hereinafter to refer to these products.
A variety of pin end thread protectors and box end thread protectors are commonly used for pipe thread protection. One common type of protector contains notches into which a straight bar can be placed and rotated to tighten or loosen. Examples of this type of thread protector are disclosed in Callicoatte, U.S. Pat. No. 4,239,062, Dec. 16, 1980; and Goodson et al., U.S. Pat. No. 7,281,546, Oct. 16, 2007. This type of protector suffers from several disadvantages. First, the notches are prone to breakage. Second, the repetitive installation and removal motion of rotating a straight bar can lead to overuse injuries. Third, the protectors are typically installed by hand at the manufacturing site as pipe section-coupling assemblies roll down transversely on a roller track. The person installing them runs the risk of having his hands injured by an adjacent pipe section-coupling assembly. Fourth, the torque applied varies when installing the protectors at the manufacturing site. Fifth, the protectors can be very difficult to remove at the point of use, especially in cold conditions when the protectors have been installed with excessive torque. Sixth, the difficulty of removal in very cold conditions often leads workers to use solvents to loosen the threads and torches to expand the plastic protectors. These steps are time-consuming and dangerous.
Other types of thread protectors are disclosed in Mirfield, U.S. Pat. No. 2,225,754, Dec. 24, 1940; Clark, U.S. Pat. No. 4,349,048, Sep. 14, 1982; Waldo et al., U.S. Pat. No. 4,487,228, Dec. 11, 1984; Kovacs, Jr., U.S. Pat. No. 7,857,007, Dec. 28, 2010; and Heritier et al., U.S. Pat. No. 8,011,391, Sep. 6, 2011. These thread protectors suffer from many of the same disadvantages of the notched protectors. Special tools to install or remove thread protectors are disclosed in Merrick, U.S. Pat. No. 4,932,292, Jun. 12, 1990; and Quick, U.S. Pat. No. 5,813,104, Sep. 29, 1998. These specialized tools fit only a particular type of thread protector.
Accordingly, there is a demand for pin end thread protectors and box end thread protectors that are durable, that are reusable, that can be installed at a constant torque without the risk of repetitive injury using commercially available tools, and that can be easily and safely removed even under cold conditions using commercially available tools.